Method of vapor growing a homogeneous monocrystal



July 9, 1968 P. s. MCDERMOTT ETAL METHOD OF VAPOR GROWING A HOMOGENEOUS MONOCRYSTAL Filed Dec. 23, 1963 2 Sheets-Sheet 2 ATMOSPHERIC 0.8 L0 L2 L4 L6 L8 2.0 2.2 24 2.6 2.8 3.0 3.2

RADIATION WAVELENGTH (MICRONS) .LOOOO OOOO I32; 2 zockoloi 1 ll|JiLlKIIllllI L50 L55 WAVELENGTH (MICRONS) FIG. 5

FIG. 4

United States Patent 3,392,066 METHOD OF VAPOR GROWING A HOMOGENEOUS MONOCRYSTAL Philip S. McDermott, Athens, Pa., and Gerald W. Manley, Oneonta, and Ralph .I. Riley and Lawrence R. Yetter, Apalachin, N .Y., assignors to International Business Machines Corporation, New York, N.Y., a corporation of New York Filed Dec. 23, 1963, Ser. No. 332,563 7 Claims. (Cl. 148-175) ABSTRACT OF THE DISCLOSURE A halogen transport process carried on in an evacuated chamber containing a growth receiving substrate and ingots of source materials together with iodine vapor. Two independently coolable heat sinks permit separate control of the temperature of the substrate and source regions of the chamber. The process involves first causing vapor transport from the substrate to the source (by controlling the temperature differential bet-ween source and substrate areas) to cleanse the growth receiving surface of the substrate. Thereafter, the process is reversed and growth is deposited on the substrate. High quality growth is achieved by maintaining substrate temperature just above the temperature at which a condensate is produced on the substrate. The vapor growth process produces high quality monocrystals of III and V valence group elements. Semiconductor devices fabricated from such crystals exhibit spontaneous and stimulated emission of radiation in the 0.9 to 3.2 micron range of wavelengths.

The process provides monocrystals of controllable composition within the system In(As P In recent years, considerable effort has been directed toward the investigation of radiation emission characteristics of various devices, and particularly to the phenomeon of stimulated emission of radiation. Devices which exhibit the capability of stimulated emission of radiation in the infrared, visible or ultraviolet regions of the radiashaped distribution covering a range of, perhaps,'0.0l

tion spectrum are known as lasers (an acronym derived I from light amplification by stimulated emission of radiation). Devices of this type are capable of producing radiation which is highly directional, coherent, and monochromatic. They have received wide publicity in the past severalyears. Utility for lasers has been found in various areas, for example, in the fields of communication, object detection and ranging, and data handling. In addition, these devices appear to have considerable utility as sources of destructive force.

Of lesser prominence, but also important, are devices which exhibit the characteristic of spontaneous emission of radiation. The radiation provided by spontaneous emission is not as highly coherent as stimulated emission, nor is it as monochromatic. Spontaneously emitted radiation or fluorescence is, however, of generally narrow bandwidth and .it is highly useful, for example, for short range communication, etc.

The establishment of spontaneous and stimulated emission of radiation involves the creation of an artificial dis;

tribution of electrons at energy levels other than the natof photonsemitted from the devicemicron; The band of emitted wavelengths is commonly referred to as the emittedfline. The line is said to have a width which is essentially the difference in wavelength between the half power points of the distribution curve The line has a central wavelength at which maximum output radiation intensity is observed and this is known as the line maximum wavelength.

Spontaneous emission is a radiative process in which the energy transitions that result in photon emission are not necessarily influenced by the presence of other similar photons. As the pumping energy is increased, emission of photons in one mode begins to occur at the'expense of other modes. It appears that emitted photons strike excited atoms and influence the emission of additional photons in fixed phase relation so that mode selectivity is achieved. This phenomenon, which is evidenced by a substantial narrowing of the emission line as well as an increase in coherency and directionality of the output radiation, is known as stimulated emission.

The host environment in which the radiation is produced may take any of several forms. In laser devices currently available in the art the host environment may be either a gas, such as helium-neon mixture or it may be a crystal of one of several different compositions. The emission has been produced by pumping energy in the form of light or, in the case of crystals of semiconductor material, the pumping energy may be supplied by injecting electrons into the semiconductor. It is toward the devices of the semiconductor type that the present invention is directed.

Spontaneous and stimulated emission of radiation from semiconductive materials is achieved by providing in the material a p-n junction and injecting minority carriers across the junction in a forward bias direction in appropriate density. The emission is produced bythe mechanism previously described in response to carrier recombination via the junction. No attempt will be made here to describe in detail the precise occurrences which result in production of radiation by carrier injection in semiconductor diode devices. A detailed explanation of the vphenomena may be found in several recent articles, for example Semiconductor Lasers, by B. Lax in Science, vol. 141, No. 3587, Sept. 27, 1963, pp. 1247-1255. Other references are cited in the copending application, Ser. No. 230,607, by Burns et a1., filed Oct. 15, 1962'and assigned to the assignee hereof.

Spontaneous and stimulated emission of radiation has been observed in semiconductor diodes of several compounds of elements in the III and V valence groups, such as gallium arsenide, indium arsenide, indium phosphide, and more recently gallium arsenide phosphide and indium gallium arsenide. The wavelength of the emission from diode devices is a function of the composition and in the case of most of those compounds mentioned above, is observed to be in the sub-micron range.

It i desirable to have the capability of producing spontaneous and stimulated emission at controlled wavelengths over a broad range. Moreover, it is desirable to provide devices capable of producing emission at wavelengths which correspond to favorable transmission regions of the spectrum in the atmosphere. These favorable regions are commonly known as atmospheric windows and they exist at various points in the radiation spectrum. Three such windows of interest to the present invention are found in the infrared region of the spectrum at wavelengths of about LZS microns, 1.6 microns, and 2.25 microns.

According to this invention there are provided means and methods for providing homogeneous single crystals structures of controlled composition within predetermined limits of a quality and perfection adequate forrealization of'spontaneous and stimulated emission over a generally broad range of wavelengths in the infrared portion of the spectrum including the portion containing the windows mentioned above. I

It has been found that by means of a novel vapor growth process, compounds embodying III-V elements may be provided in the form of homogeneous single crystails of high quality and perfection. Moreover, it has been found that by means of this process, the composition of the final compoundcan be controlled within relatively close tolerances so that devices capable of producing emission at predetermined wavelengths can be fabricated.

' This novelprocess has been employed to provide'homogeneoussingle crystal compounds'of controlled composition in the system of In(As P' hitherto unknown in this form. Devices fabricated from crystals of compositions in this system display emission wavelengths which vary from 0.9 micron (the emission wavelength of InP) to 3.2 microns (the emission wavelength of InAs).

Accordingly, it is a primary object of this invention to provide homogeneous single crystals of controlled composition and of quality and perfection adequate for use as spontaneous and stimulated emission sources.

Another object of the invention is to provide improved means and methods of growing homogeneous single crystals of controlled composition.

A further object of the invention is to provide an improved method for producing compounds of controlled composition within the system In(As P in the form of homogeneous single crystals of desired size.

Still another object of the invention is to provide means for growing homogeneous single crystals of controlled composition and for imultaneously doping said crystals with selected impurities.

Another primary object of the invention is to provide novel solid state devices for producing spontaneous and stimulated radiation in the infrared portion of the radiation spectrum.

It is also an object of this invention to provide novel solid state light sources of controlled frequency in the 0.9 to 3.2 micron range.

It is also an object of this invention to provide improved injection diodes for emitting radiation.

A further object of the invention is to provide injection diodes having out-put radiation wavelengths which correspond to favorable transmission regions or atmospheric windows in the infrared portion of the radiation spectrum.

The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings.

In the drawings:

FIG. 1 is a perspective view illustrating the crystal growing apparatus provided in accordance with this invention;

FIG. 2 is a longitudinal vertical sectional view taken through the reaction chamber which forms part of the apparatus of FIG. 1;

FIG. 3 is a diagrammatic illustration of an injection diode provided in accordance with this invention;

FIG. 4 is a graph showing the bandwidth of radiation produced in the cases of spontaneous and stimulated emission from a typical diode provided in accordance with this invention; and

FIG. 5 is a graph showing the corelation between radiation wavelength and composition for diodes provided in accordance with this invention.

The phenomena of spontaneous and stimulated emis sion of radiation have been observed in several semicon ductive materials, as described hereinbefore. One of the characteristics of a semiconductive material necessary for the establishment of these phenomena is a homogeneous single crystal/structure of high; quality and perfection. According to this invention means and methods have been developed by which 'semiconductive compoundsof "elements'in the IH and V valence groups of-the Mendeleefi periodic chart can be grown in the form at single crystals of desired size and of a quality and perfection 'suitable for establishment of spontaneous andfstimulatedemission. The meansand methodsof this invention havebeen employed to produce novel high ,quality homogeneous single crystals of controlled composition in the system In'(As P The process by which crystals are grown inaccordance with this invention is a vapor transport process by which elements are caused to be deposited by disproportion tion reaction on a substrate from source materials at temperatures lower than the melting points of the elements involved. The principles of vapor growth and disproportionation reactions are known in the art'and will not be discussed in detail herein. Detailed information on this subject is available in a group of five articles in' the IBM Journal of Research and Development, vol. 4, No. 3, July 1960, at pages 248 through 279, andin the references listed in these articles. It is sufiicient foran understanding of this invention to say-simply that the disproportionation reaction involves the transport of materials in the form of vapor phase iodides (iodine being the transport agent) from source materials at one temperature to a receiving substrate at a lower temperature.

The improved vapor growing process of this invention is carried out with the apparatus shown in FIGS. 1 and 2 of the drawing. The apparatus includes a quartz chamber 10 having a generally semicylindrical outline with a flattened floor section 12. At one end of the chamber 10 a flat transparent quartz end wall 14 is fused to form a viewing window and to seal that end of the chamber. The opposite end is initially open to permit the various materials to be used in the growing process to be loaded. The chamber is evacuated and this end of the chamber is eventually sealed by fusing a-quartz plug 16 in place, as shown in FIG. 2.

The reaction chamber 10 is arranged to have two temperature regions, as will be explained more fully later herein, and these are provided by attaching beneath the floor 12 of the chamber at spaced points a pair of metallic blocks 18 and 20 to act as heat sinks. The heat sinks 18 and 20 are held in place by bands 19'and 21 as shown. These heat sinks are preferably fabricated of a substance such as silver which has high conductivity and will withstand the temperature involved.

The heat sinks 18 and 20 have fluid conducting apertures 22 formed therein and fluid lines 24 and'26 are connected thereto to permit circulation of cool-ant, such as air, through the sinks. The fluid lines 24 and 26 are coupled to suitable circulating means (not shown) for pumping coolant through the heat sinks 18 and 20. The circulating means for the line 24 is independent of the means for the line 26 so that different temperatures can be maintained at the heat sinks 18 and 20. Temperature sensing means 28 and 30 are provided'for accurately detecting the temperature of the heat sinks 18 and 20. In the embodiment shown in FIGS. 1 and 2 these sensing means are in the form of thermocouples contacting the metallic heat sinks. The thermocouples are connected to suitable temperature registering means (not shown). I

The heat sinks 18 and 20 and their-associated temper ature control and indicating means provide two regions of variable temperature in the chamber 10. The region adjacent the sink 18 is a deposition regionand that adjacent the sink 20 is a source region. Into the chamber immediately above the heat sink Bis-placed a substrate32 upon which the crystal is to be grown, and'above the heat sink 20 are placed pieces 34 and 36 of the materialswhich are to be used as sources. I

To insure growth of a monocrystal of high quality and perfection the substrate 32 must be carefully prepared. It is essential that the substrate 32 be itself a monocrystal and that it be out along crystallographic planes to provide a growth receiving surface .33 aligned along a'desired plane. The substrate need not be of the same composition as the crystal to be grown thereon. The substrate should be of a material having a lattice spacing similar .to that of the crystal to be grown.

' In the growing processes performed in accordance with this invention substrates of monocrystal indium arsenide were used. These substrates were cut from monocrystal ingots previously aligned by X-ray techniques, to provide growth receiving surfaces along the (100) crystallographic plane. The receiving surface 33 of each substrate 32 is polished using a glass plate and an abrasive of 600 mesh SiC, and then buffed with an alcohol and bromide mixture on 0.1 micron grit polishing paper.

The donor or source pieces 34 and 36 are obtained as ingots includingall of the elements to be combined in the deposited crystal. In growing crystals of the system In(As P ingots of InAs and InP are employed. The ingots may be polycrystalline and need not be out along crystallographic planes. It has been found that the composition of the grown crystal is proportional to the respective areas of the ingot surfaces which face the substrate in the reaction chamber.

It appears that the etching of the source materials occurs primarily at these faces, although some etching of the top and side surfaces is also observed. The relation of face area to final composition is suificient, however, to permit composition control to within tolerances in the order of a few percent. Accordingly, the source ingots 34 and 36 are cut so that the areas of faces 35 and 37 are in proportion to the desired composition of the final product. For example, if a crystal of In(As P is desired,

the areas of the faces 35 and 37 of the ingots are made equal. If a crystal of In(As P then the ingots 34 and 36 are cut so that the areas of faces 35 and 37 provide the ratio 2:8.

The source ingots 34 and 36 are polished with glass plates and 600 mesh SiC abrasive and cleaned with an alcohol bromide solution to insure that all surfaces thereof are regular and free of foreign material. They are then placed in the chamber directly over the heatsink-ZO with the surfaces and 37 facing the substrate. 7

The crystal grown in the reaction chamber is simultaneously doped as it is grown, so it is necessary to provide in the chamber an amount of doping material. The doping material is chosen in accordance with the type of impurity desired in the crystal. For growing an n-type- Once the iodine vessel is evacuated, it is immersed in liquid nitrogen to prevent sublimation of the iodine, and pumping is resumed to return the chamber to 10- torr. Then the chamber is immersed in liquid nitrogen and the iodine vessel is gently heated to cause the iodine to be transferred to the chamber 1 0 by distillation. "Following this, the plug 16 is fused in place to seal the chamber and the connection to the vacuum system is broken.

.The iodine loading process just described is but one of several processes which may be employedfor the purp0se. Those familiar with the vapor growing art Willrecognize that other processes are also available.

After the reaction chamber has been loaded, evacuated, and sealed the heatsinks 18 and 20 are secured in place and the apparatus is placed in a furnace, for example, a clam shell furnace 38 is shown in FIG. 1. The furnace isclosed and sealed to prevent undesirable air currents around the chamber 10. In sealing the furnace it is necessary to provide a viewing port to permit visual access to the chamber interior through the window 14. The viewing port may take the form of a quartz plate at the left end of the clam shell furnace 38.

The growth process is initiated by heating the furnace to a temperature of about 830 C. The furnace is held at this temperature for the duration of the process. During the heating process, the interior of the chamber 10 Will be observed to take on first an iodine violet color and then the yellowish color characteristic of indium iodides.

As the temperature within the reaction chamber builds up the coolant controls for the heat sink 20 are operated to reduce the temperature of the source area. Sufficient coolant is circulated to maintain the source area about 100 C. below the ambient furnace temperature. The deposition region is not cooled appreciably. It may be maintained a few degrees below the ambient furnace temperature to provide for positive control in either direction. The purpose of cooling the source region is to produce some vapor transport from the substrate to the source to clean the surface 33, and to insure that any undesirable low temperature reaction products are condensed in the source region and do not contaminate the substrate. As the temperature increases above about 500 C. the upper surface of the substrate is observed to change texture and become substantially glossy. This change in appearance occurs in response to etching of the surface by the iodine vapor. This etching of the substrate surface cleans it in preparation for the subsequent deposition and is found to be necessary to insure growth of a high quality crystal. While etching commences with the surface of the substrate facing the source region, sufiicient etching I occurs at the surface 33 to clean it before the front is appreciably eaten away.

The pre-etching process does not require a substantial time and may be considered complete after about 10 The transport agent used is semiconductor grade iodine;

Because of the low melting point of this substance, care must be exercised to avoid its beingevaporated away during evacuation of the chamber 10. To prevent this, the chamber 10 is evacuated, by connection to the manifold of a-vacuum pump (not shown), before the iodine is introduced. The'iodine is placed in a separatevessel which is also connected to the-manifold through a valve which is initially closed. After the chamber 10 has been minutes or when the substrate surface has taken on a uniform glossy appearance. The process will usually be complete by the time the furnace has reached 800 C. At this time, the supply of coolant to the source area heat sink 20 is diminished and it is allowed to approach the furnace temperature within a few degrees. At this time coolant is circulated through the heat sink 18 at the deposition region of chamber 10 to cool that area. As the temperature at the source region builds, substantial etching of the source ingots 34 and 36 is observed.

Coolant is supplied to the deposition region heat sink in sufficient quantities to lower the temperature of that region below the dewpoint of the iodides present in the chamber, as evidenced by the formation of a condensate upon the surface of the substrate. When this occurs, the coolant flow is carefully diminished to allow the temperature at the deposition region to increase slowly. As the dewpoint temperature is passed, the condensate on the substrate 32 will disappear. This temperature, which may vary somewhat due to differences in proportions of source materials present and to dopant concentrations, etc., may

be determined within suflicient tolerances by reading the temperature of the heat sink 18 at the time the condensate disappears.

The deposition region temperature is allowed to increase only slightly (about to C.) above the indicated dewpoint and then the coolant flow is adjusted to hold a constant temperature. This temperature is considerably below that at the source region, as shown in the 3rd and 4th columns of Table 1. Under these conditions, a monocrystal of composition controlled in accordance with the source 'ingotproportions, as explained earlier, and doped with the impurity provided, will be observed to grow on the substrate. If the conditions have been properly established, good uniformity of growth will be observed. The quality of the crystal is visually determined by noting uniform glossy growth over the entire surface of the substrate. If some condition occurs which interferes with the growth process, as evidenced by condensation occurring or growth of spurious crystallites, then minor compensating adjustments may be made in the temperature of the source and deposition regions by coolant control. It may, at times, be necessary to temporarily invert the temperatures of the two regions to reverse the growth process and remove imperfect growths. This can be readily accomplished with the novel apparatus provided in accordance with this invention. After such removal, the initial growing conditions are reestablished as previously described.

At the end of the growing process, which may be from about 5 hours to 20 hours for monocrystal of about 0.5 gm., the furnace power is discontinued and the system is allowed to cool down. At this time, the flow of coolant to heat sink 18 is diminished and the deposition region is allowed to approach chamber temperature. Coolant is supplied to the source region heat sink 20 at this time to cool it down considerably faster than the remainder of the system. This action insures termination of growth at the substrate and causes all remaining reaction products to be precipitated at the source region to prevent possible contamination of the grown crystal.

The particulars of a number of actual growth processes which produced high quality monocrystals are shown in Table I. The figures shown in this table are to be considered as exemplary only and are not intended to limit the invention except insofar as it is limited by the claims.

It will be seen from the examples in the table that any desired composition in the In(As P system may be produced in the form of high quality homogeneous monocrystals.

Diodes are fabricated from the crystals produced in accordance with this invention, in a known manner. A typical procedure for fabricating a diode such as'the one shown in FIG. 3, from a crystal doped with n-type impurity is described below.

The substrate containing the grown homogeneous single crystal layer is first oriented by use of an X-ray difiractometer, for example, to enable the crystal to be cut to provide a surface along the (100) crystallographic plane. The crystal is ground and polished along thisplane to provide a surface free of defects and imperfections. The surface will become the face 40 of the finished diode. After polishing, the crystal is washed, dried, and prepared for diffusion of a junction therein. I

For diffusion, the crystal is sealed in a quartz container containing a small quantity of zinc arsenide', for example 2 mg. for a container of 6 cc., and the container is evacuated to about 10" torr. The container is thereafter heated in a furnace at about 650 C. for a period of about two hours. During this period, the zinc diffuses into the crystal from the various surfaces including the polished (100) plane surface, forming a p-type region in the n-type crystal. A junction, shown at 42 in FIG. 3,parallel with the (100) plane is formed between the p and 11 regions at a depth of about 1 mil from the polished surface.

After diffusion, the crystal is ground to provide a surface along the (100) plane on the side of the crystal opposite the previously polished surface. This will become the surface 44 of the finished diode. The grinding is carried to.a depth sufficient to insure removal of any p-type material created on that side of the material and to reduce the thickness between the opposed surfaces to the order of about 5 mils.

Following the grinding operation the crystal, now in the form of a 5 mil thick wafer, is again washed and dried and provided with ohmic metallic contacts 46 and 48 on the (100) plane surfaces 40 and 44 by any known means, for example, electroless deposition.

It is desirable that the finished diode have end surfaces 50 and 52 perpendicular to the junction which are optically flat and parallel to each other. The purpose of these surfaces is to reflect a portion of the radiation produced in the junction region and to reinforce the emission in a known manner. While these surfaces may be produced by grinding and polishing, it is preferable to produce them by cleaving the crystal along the (110) crystallographic plane. The wafer is cleaved to provide two end surfaces along the (110) plane spaced about 17 mils apart.

TABLE I Source Area Substrate Area Dopanr Concen- Crystal Hall Constant Sample Composition Temp. During Temp. During tration in Crystal Resistivity (co/coulomb) Growth 0.) Growth C.) (carriers/cc.) (ohm-cm.)

MRM 18 InAS Te-3.9X10 9. 73x10 0.161

MRM 19 In(As.s2P.ia) 820 760 'le-2.3X10" 9. 74x10 0.273 MRM 20 II1(AS H5PJ5) 840 760 Tet-3. 3X10" 22. 6X10 0. 192 785 Te-l. 4X10" 5. 79X10 0. 441 760 Tet-2. 6X10 13. 7X10" 0. 230 700 Te-l. 8X10 l 66Xl0 0. 336 MRM 25 In(AS.a4P.1a 780 Tie-22x10 6 34x10 0.281 MRM 26 In(AS.41P.59) w 720 Te-1.4 10 2. 26Xl0" 0.445 MRM 28 ID(AS 13P 32) 820 605 Te-G. 8X10 6. X10 0. 918

In all of the examples of Table I the growth process was carried out under the general condition described hereinbefore. The substrate-to-source distance was varied slightly in'sorne cases but was always less than one inch. This spacing was not found to be particularly critical.

As indicated earlier herein, only general control of the doping concentration is available when the dopant is free in the chamber 10. If more precise control is desired, a crystal may be grown from a pair of source crystals, one of which has been previously doped to a known extent, and the other of which is undoped. By varying the proportions of the doped and undoped source crystal, any dopant concentration may be achieved.

The two side edges 54 and 56 of the finished diode are produced by sawing.

The completed diode shown on FIG. 3, is provided with suitable electrical conductors 58 and 60 which are attached to the ohmic contact surfaces 46 and 48, to provide means for injecting carriers therein.

Diodes fabricated as just described are operated as radiation emitting devices by injecting current thereto via the electrodes from a power source 62. Spontaneous emission of radiation from these diodes hasbeen achieved with injection current densities as low as 525 amp per square centimeter attemperatures of 77 K. and at injec tioiicurrentdensities of 600 amp/cm. at'room temperature. Stimulated emission, or true laser ac'tion, is' achieved with current densities ofas low as 6400 amps persquare centimeter at temperatures of 77 K; for a typicalsample. B'o'th spontaneous and stimulated emission have been obtained-in th'eabsence of any magnetic field. H

TableII gives data relating to actual operation of diodes fabricated from crystals grown in accordance with this invention. In Table II the leftmost" column-indicates the crystal sample from which thedi'odjeiwas fabricated. Table :I gives the growth information concerningithat sample.

crystals are unique in-the provisionof independent control of the conditions at-the' source and substrate regions of the growth chamber, so that 'precleaning of the substrate is possible, so that low temperature reaction products may be kept away from the'substrate-bothduring the heat-up. and cooling phases of thegrowth process, and so that conditions may be adjusted during growth. Another unique feature resides in the ability .toview the process throughoutits duration to monitor the growth and determine the actions. tobe takento maintainoptimum growth conditions. Another unique featurezof. the growth process resides in the recognitionthat growth of TABLE II i i d :Spontaneous Emission Data Stimulated Emission Data e I Sample Temp. Current Line Max. Line Width Current Line Max. Line Width K.) Density, Wavelength (microns) Density W'avele'ngth (microns) amp/cm. (microns) amp/cm.

MRM 1s. 77 1,050 3:25 0.24 MRM 19... 77 2, 820 g 2. 27 0. l2 MRM 19 4" 3,300 23 0.08 MRM 20- 4 2, 400 2. 47 0.13 MRM 21..- 300- 600 1.71 0.18 MRM 21-.. 77 525 1161. 0 06 MRM 4 4,000 1. 59 0 02 MRM 2l .7 2 MRM 23. 4 1, 200 2. 19 0. 09 MRM 25--. 4 3,900 2. 33 0.14 MRM 26. 77 1, 500 1 4a 0. 05

For all samples shown in the table'above, the spontaneous emission was produced by injection current in the p jection current pulses having a duration of 50 nanoseconds and a repetition rate of 60 pulses per second. In the 4 K. and 2 K. tests of MRM21 pulses of 500 nanoseconds duration and a repetition rate of 100 p.p.s. were employed.

Examination of Table II shows the Wide range of radiation wavelengths that are obtained with diodes provided in accordance with this invention. While data was not obtained for stimulated emission in all cases, the several examples of laser action which are given indicate the presence of a substantial range.

-It will be noted that the line width obtained for the laser beam of the diode of MRM21 material when operated at 2 K. is extremely narrow. Since the wavelength of this material corresponds with one of the atmospheric windows in the infrared, it may be expected to be of significant importance.

It is also interesting to note that the MRM21 diode displayed spontaneous emission at a reasonable current density at room temperature. The ability to emit light at this temperature is unique and, of course, of considerable importance.

FIG. 4 of the drawings illustrates the emission characteristics of the MRM21 diode at 77 K. It will be observed that the spontaneous emission distribution curve 64 has the characteristic bell shape. The line Width for spontaneous emission is about 600 Angstrom units. When the stimulated emission threshold is passed, the line narrows significantly (to about 23 Angstrom) as shown by curve 66, and the peak intensity goes up considerably.

FIG. 5 of the drawings illustrates the peak wavelengths of the various crystals grown in accordance with this invention. As shown in the chart, a substantially complete spectra of wavelengths between the InAs and InP wavelengths is provided. Any selected radiation wavelength may be obtained simply by adjusting the AsrP ratio in the crystal grown in accordance with this invention.

It is believed to be apparent from the foregoing that the present invention provides the capability of producing high quality homogeneous monocrystals of controlled composition from which radiation emitting diodes may be fabricated. The means and methods for providing such In(As P compounds is best achieved when the substrate region temperature is .only slightly above the dewpoint of the species present in that region of the chamber.

While the process has been described as employing iodine as the transfer agent, and indium, arsenic and phosphorus as the growth elements it will be understood that other halogen elements may be employed for transport, and that other III and IV group elements may be grown.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A method of vapor growing a homogeneous monocrystal of controlled composition in III and V valence 8 groups comprising:

enclosing source materials containing elements to be grown into said monocrystals in an evacuated chamber with a growth receiving substrate and a predetermined quantity of a halogen transport medium; heating said chamber to a temperature at which a halogen disproportionation reaction takes place;

then lowering the temperature of the substrate to the dewpoint of the halides present in the chamber whereby condensate is detectable on the surface of the substrate; then slowly increasing the temperature of the substrate to less than 10 C. above the dewpoint temperature whereby condensate is caused to disappear;

then maintaining the substrate at said temperature above the dewpoint temperature, at which a uniform glossy appearance is observed over the entire surface of the substrate until a crystal of desired size has been deposited on the substrate.

2. A method of vapor growing a homogeneous crystal in accordance with claim 1 in which said method further includes:

discontinuing heating of said chamber and allowing it to cool, terminating temperature control of said substrate whereby the temperature rises to the temperature of said chamber, and lowering the temperature of the source materials below the temperature of the substrate whereby crystal growth on said substrate is terminated and any remaining reaction products in said chamber are caused to become deposited on said source materials.

3. A method of growing a homogeneous monocrystal in accordance with claim 1 wherein a predetermined amount of a selected semiconductor impurity element is enclosed in said chamber to cause said grown crystal to include a predetermined impurity concentration.

4. A method of growing a homogeneous monocrystal in accordance with claim 1 in which said source materials are ingots and wherein the areas of the surfaces of the ingots facing the substrate are arranged to have the same proportion that the elements in those ingots are desired to have in the grown crystal. 1

5. A method of growing homogeneous monocrystals in accordance with claim 4 where the ingots contain the elements indium, arsenic and phosphorus.

6. A method of vapor growing a homogeneous monocrystal in accordance with claim 4 in which:

said temperature of said chamber is between 750 C.

and 900 C.; said source materials are ingots comprised of indium arsenide and indium phosphide; and said substrate is a monocrystal of indium arsenide.

7. A method of vapor growing a homogeneous monocrystal of the composition In'(As 'P where x is a selected value greater flian zero and less than one, said method comprising:

enclosing ingots containing indium, arsenic, and phosphorus in an evacuated chamber with a growth receiving substrate and a predetermined quantity of iodine; heating said chamber to a temperature between about 750 C. and 900 C.;

first controlling the temperature of the region of the chamber containing the ingots so that'it remains substantially below the temperature of the substrate containing region of the chamber to cause the surfaces of the substrate to be etched and-toinsure that spurious reaction products are--not= deposited upon the substrate; then allowing the temperature. of the ingot containing 5 region of the chamber to approach the temperature to which the chamber ish'eated and controlling-"the temperature of the region of thechambencontain ing the substrate to reduce "itsufiiciently below the chamber temperature to produce a condensate upon thesubstrate; and

then raising the temperature of the' regior'i of the charnber containing "the substrate until-the condensate disappears and maintaining the" region containing the substrate at a temperature up to' lfl fl'abovo the temperature which the-condensate disappears; until a crystal of desired size has'been-deposited uponthe substrate.

,RefereucesCited 2o 7 UNITED STATES PAT ENTS V 3,14s;o94 9/1964 Kendall 148 17,; 3,218,205 11/1965 Ruehrwein 148 17 5 3,224,911 12/1965 VWilliamset a]. 148 -17 5 3,224,913 12/1965 Ruehrwein 148,-.-1 I 5 REFERENCES Marinace IBM TechnicalDisclosure Bulletin, Vol.3, No.8, January 1961, p. 33. v HYLAND BIzoT, Pririrary Examiner.

DAVID L. RECK, JEWELL H.- PEDERSEN, .Ernmiiiers;

N. F. MAkKVA, P. R. MIL'LER, P. WEINSTEIN, f

Assistant Eramirters. 

